Recentered importance sampling with applications to Bayesian model validation

Since its introduction in the early 1990s, the idea of using importance sampling (IS) with Markov chain Monte Carlo (MCMC) has found many applications. This article examines problems associated with its application to repeated evaluation of related posterior distributions with a particular focus on Bayesian model validation. We demonstrate that, in certain applications, the curse of dimensionality can be reduced by a simple modification of IS. In addition to providing new theoretical insight into the behavior of the IS approximation in a wide class of models, our result facilitates the implementation of computationally intensive Bayesian model checks. We illustrate the simplicity, computational savings, and potential inferential advantages of the proposed approach through two substantive case studies, notably computation of Bayesian p-values for linear regression models and simulation-based model checking. Supplementary materials including the Appendix and the R code for Section 3.1.2 are available online

Dynamics of the spread of the Bovine Viral Diarrhoea Virus (BVDV) within a dairy herd according to the separation of animals into subgroups

International audienc

Effect of time-dependent transitions for dynamics of structured populations in epidemiological models

International audienceIn structured livestock populations like cattle herds, movements between groups of animals often depend on age or physiological status of animals, thus on the time spent in a group. In epidemiological models, transitions between groups are usually assumed Markovian (independent on the time spent in the group). Our objective was to study the effect of a transition between groups under a triangular distribution of the transition time on the pathogen spread within a structured livestock population, compared to the effect of a Markovian transition under an exponential distribution. A SIR stochastic model was defined for a population separated into youngstock and adults. Due to the separation into groups, an heterogeneity of the pathogen transmission was assumed: direct transmission within each group and indirect transmission between groups The pathogen spread after an introduction of a newborn infected animal was simulated both with an exponential (Markov) and a triangular distribution for the youngstock to adults transition time. These two distributions may lead to significant differences in the epidemic size both in the youngstock group and in the adult group. But, at the population level, the epidemic sizes were not significantly different. The persistence of the pathogen was not significantly different

Effect of time-dependent transitions for dynamics of structured populations in epidemiological models

International audienceIn structured livestock populations like cattle herds, movements between groups of animals often depend on age or physiological status of animals, thus on the time spent in a group. In epidemiological models, transitions between groups are usually assumed Markovian (independent on the time spent in the group). Our objective was to study the effect of a transition between groups under a triangular distribution of the transition time on the pathogen spread within a structured livestock population, compared to the effect of a Markovian transition under an exponential distribution. A SIR stochastic model was defined for a population separated into youngstock and adults. Due to the separation into groups, an heterogeneity of the pathogen transmission was assumed: direct transmission within each group and indirect transmission between groups The pathogen spread after an introduction of a newborn infected animal was simulated both with an exponential (Markov) and a triangular distribution for the youngstock to adults transition time. These two distributions may lead to significant differences in the epidemic size both in the youngstock group and in the adult group. But, at the population level, the epidemic sizes were not significantly different. The persistence of the pathogen was not significantly different

Dynamics of the spread of the Bovine Viral Diarrhoea Virus (BVDV) within a dairy herd according to the separation of animals into subgroups

International audienc

Influence de la structuration du troupeau en lots sur la propagation du virus de la Diarrhée Virale Bovine (BVDV) en élevage bovin laitier

National audienceThe spread of the Bovine Viral Diarrhoea Virus (BVDV) within a herd is influenced by the herd management. In dairy herds, animals are distributed into subgroups and this induces an heterogeneity in the probability of BVDV transmission. This paper presents a study of the influence of the level of separation between subgroups on the BVDV spread. A simulation model of the BVDV spread was used. In a totally susceptible herd, a freshening non-PI heifer with a PI fetus was introduced. The BVDV spread was simulated assuming different levels of contacts between subgroups (no contact, intermediate or high level of contacts). The influence of this level of contacts between subgroups on the probability of BVDV transmission was considered by defining different BVDV transmission rates. In the results, the BVDV persistence, the extent of infection and the variability of the dynamics of the BVDV spread were found to be influenced by the level of contacts between subgroups. Therefore, the separation of animals into subgroups has to be taken into account to model the BVDV spread in order to assess the control programsLa propagation du virus de la Diarrhée Virale Bovine (BVDV) dans un troupeau est influencée par la structure du troupeau. Dans les troupeaux laitiers en particulier, les animaux sont conduits en lots plus ou moins fortement séparés. Ceci induit une hétérogénéité de la probabilité de transmission du virus et pourrait conduire à accroître la variabilité des dynamiques de propagation. L’objectif de cette étude est d’évaluer l’influence du degré de séparation entre lots sur les dynamiques de propagation du virus BVDV. Un modèle de simulation de la propagation du virus BVDV a été utilisé. Dans un troupeau sans exposition antérieure au virus, une génisse non Infectée Permanente Immunotolérante (IPI) portant un fœtus IPI a été introduite. Différents niveaux de contacts entre lots (absence, intermédiaire, élevé) ont été simulés. L’effet du degré de séparation entre lots sur la transmission horizontale du virus a été pris en compte par des taux de transmission différents. Dans les résultats, la persistance du virus, l’étendue de l’infection et la variabilité des dynamiques de propagation sont influencées par le degré de séparation. La structuration en lots et le degré de séparation doivent donc être pris en compte pour la modélisation de la propagation du virus BVDV en vue de l’élaboration de plans de maîtris

Influence de la structuration du troupeau en lots sur la propagation du virus de la Diarrhée Virale Bovine (BVDV) en élevage bovin laitier

National audienceThe spread of the Bovine Viral Diarrhoea Virus (BVDV) within a herd is influenced by the herd management. In dairy herds, animals are distributed into subgroups and this induces an heterogeneity in the probability of BVDV transmission. This paper presents a study of the influence of the level of separation between subgroups on the BVDV spread. A simulation model of the BVDV spread was used. In a totally susceptible herd, a freshening non-PI heifer with a PI fetus was introduced. The BVDV spread was simulated assuming different levels of contacts between subgroups (no contact, intermediate or high level of contacts). The influence of this level of contacts between subgroups on the probability of BVDV transmission was considered by defining different BVDV transmission rates. In the results, the BVDV persistence, the extent of infection and the variability of the dynamics of the BVDV spread were found to be influenced by the level of contacts between subgroups. Therefore, the separation of animals into subgroups has to be taken into account to model the BVDV spread in order to assess the control programsLa propagation du virus de la Diarrhée Virale Bovine (BVDV) dans un troupeau est influencée par la structure du troupeau. Dans les troupeaux laitiers en particulier, les animaux sont conduits en lots plus ou moins fortement séparés. Ceci induit une hétérogénéité de la probabilité de transmission du virus et pourrait conduire à accroître la variabilité des dynamiques de propagation. L’objectif de cette étude est d’évaluer l’influence du degré de séparation entre lots sur les dynamiques de propagation du virus BVDV. Un modèle de simulation de la propagation du virus BVDV a été utilisé. Dans un troupeau sans exposition antérieure au virus, une génisse non Infectée Permanente Immunotolérante (IPI) portant un fœtus IPI a été introduite. Différents niveaux de contacts entre lots (absence, intermédiaire, élevé) ont été simulés. L’effet du degré de séparation entre lots sur la transmission horizontale du virus a été pris en compte par des taux de transmission différents. Dans les résultats, la persistance du virus, l’étendue de l’infection et la variabilité des dynamiques de propagation sont influencées par le degré de séparation. La structuration en lots et le degré de séparation doivent donc être pris en compte pour la modélisation de la propagation du virus BVDV en vue de l’élaboration de plans de maîtris

SET translocation is associated with increase in caspase cleaved amyloid precursor protein in CA1 of Alzheimer and Down syndrome patients.

Caspase cleaved amyloid precursor protein (APPcc) and SET are increased and mislocalized in the neuronal cytoplasm in Alzheimer Disease (AD) brains. Translocated SET to the cytoplasm can induce tau hyperphosphorylation. To elucidate the putative relationships between mislocalized APPcc and SET, we studied their level and distribution in the hippocampus of 5 controls, 3 Down syndrome and 10 Alzheimer patients. In Down syndrome and Alzheimer patients, APPcc and SET levels were increased in CA1 and the frequency of both localizations in the neuronal cytoplasm was high in CA1, and low in CA4. As the increase of APPcc is already present at early stages of AD, we overexpressed APPcc in CA1 and the dentate gyrus neurons of adult mice with a lentiviral construct. APPcc overexpression in CA1 and not in the dentate gyrus induced endogenous SET translocation and tau hyperphosphorylation. These data suggest that increase in APPcc in CA1 neurons could be an early event leading to the translocation of SET and the progression of AD through tau hyperphosphorylation

O R I GI N A L A R T IC L E

Abstract Objectives: From August 1st to 20th, 2003, the mean maximum temperature in France exceeded the seasonal norm by 11-12°C on nine consecutive days. A major increase in mortality was then observed, which main epidemiological features are described herein. ,000 excess deaths were observed. From 35 years age, the excess mortality was marked and increased with age. It was 15% higher in women than in men of comparable age as of age 45 years. Excess mortality at home and in retirement institutions was greater than that in hospitals. The mortality of widowed, single and divorced subjects was greater than that of married people. Deaths directly related to heat, heatstroke, hyperthermia and dehydration increased massively. Cardiovascular diseases, illdefined morbid disorders, respiratory diseases and nervous system diseases also markedly contributed to the excess mortality. The geographic variations in mortality showed a clear age-dependent relationship with the number of very hot days. No harvesting effect was observed. Conclusions: Heat waves must be considered as a threat to European populations living in climates that are currently temperate. While the elderly and people living alone are particularly vulnerable to heat waves, no segment of the population may be considered protected from the risks associated with heat waves